Incident Overview

Date: Friday 11 June 1999
Aircraft Type: Boeing 777-222
Owner/operator: United Airlines
Registration Number: N781UA
Location: Madison, WI – ÿ United States of America
Phase of Flight: Unknown
Casualties: Fatalities: 0 / Occupants: 296
Component Affected: Flight seat belt sign.Flight seat belt sign.
Investigating Agency: NTSBNTSB
Category: Accident
A flight experienced turbulence at an altitude of 19,680 feet msl during a descent from Minneapolis to Chicago. Four passengers and flight attendants sustained minor injuries, including a broken ankle. The flight was diverted to Minneapolis due to thunderstorm activity in the Chicago area. The pilot-in-command reported a smooth flight until the turbulence, which was triggered by a stationary front extending northeast-southwest through central Wisconsin and Iowa. The flight crew received a Weather Briefing Message (WBM) prior to departure, which included convective segments for the affected area. A review of the Quick Access Recorder revealed a change in G-loading from 0.0843 g’s to 1.9375 g’s over a short period.A flight experienced turbulence at an altitude of 19,680 feet msl during a descent from Minneapolis to Chicago. Four passengers and flight attendants sustained minor injuries, including a broken ankle. The flight was diverted to Minneapolis due to thunderstorm activity in the Chicago area. The pilot-in-command reported a smooth flight until the turbulence, which was triggered by a stationary front extending northeast-southwest through central Wisconsin and Iowa. The flight crew received a Weather Briefing Message (WBM) prior to departure, which included convective segments for the affected area. A review of the Quick Access Recorder revealed a change in G-loading from 0.0843 g’s to 1.9375 g’s over a short period.

Description

While en route from Minneapolis to Chicago the flight encountered turbulence at 19,680 feet msl while in a descent. Four passengers and four flight attendants received minor injuries. One passenger received a broken ankle. The flight had diverted to Minneapolis due to thunderstorm activity in the Chicago area. The captain reported the flight was smooth up until the unexpected turbulence was encountered. The seat belt sign was not on at the time of the encounter. The flight crew received a Weather Briefing Message (WBM) prior to departing Minneapolis, which contained convective sigmets for Wisconsin, Illinois, and Indiana. The accident took place ahead of a stationary front which extended northeast-southwest through central Wisconsin and Iowa which had been creating shower and thunderstorm activity throughout afternoon and evening on the day of the accident. A review of the data from the Quick Access Recorder revealed the flight experienced a change in G-loading from .0843 g’s to 1.9375 g’s over a 2-second time period while at an altitude of 19,680 feet msl. Probable Cause: the pilot-in-command’s inadequate evaluation of the weather conditions. Factors associated with the accident were the turbulence encountered and the seat belt sign was not illuminated.

Primary Cause

Inadequate evaluation of weather conditions by the pilot-in-command.Inadequate evaluation of weather conditions by the pilot-in-command.

Share on:

Leave a Reply

Your email address will not be published. Required fields are marked *